The increased use of metal-to-metal sealing means for wellhead annulus seals has created a need for means for generating the large compressive loads needed typically to energize these seals. Additionally, the problem exists of how to retain this large compressive load in the seal after the load generating means has been removed. A possible solution would require that the drill pipe used to lower the sealing means into position be rotated while pressure was being applied in the annular region between the sealing means and the rams of the blowout preventer. Such rotation of the drill pipe while the pipe rams of the blowout preventer are closed and subjected to pressure is considered highly unacceptable by some operators.
Alternatively, in an effort to avoid rotating the drill pipe with the pipe rams closed, some prior inventions have employed various complex hydraulic or mechanical means to allow compression and locking of the sealing means. These devices have had various shortcomings such as requiring excessive drill pipe rotation, requiring precise location of the tool within the wellhead housing, or lacking sufficient capacity to generate the force required to activate the seal.
This invention is for an improved seal installation tool and lockdown mechanism that generates a sufficiently large load for setting metal-to-metal wellhead annulus seals. It does not require the rotation of drill pipe while the rams of the blowout preventer are under pressure. The lockdown mechanism locks the preload into the seal as the seal is energized. The invention is particularly suited for use with metal-to-metal seals requiring high compressive loads for setting.
Prior packoff installation tools and lockdown mechanisms included the torque type mechanism disclosed in the A.G. Ahlstone et al. U.S. Pat. No. 3,350,130. The Ahlstone installation tool structure allows the seal assembly to be lowered to the wellhead and tightened by rotation of the drill pipe prior to testing.
The C.C. Brown U.S. Pat. No. 3,357,486 discloses another seal setting structure which allows for either mechanical or hydraulic actuation of the seal assembly. The Brown invention requires the seal setting structure to be aligned with a groove in the wellhead housing for proper orientation and operation.
The J.A. Haeber U.S. Pat. No. 3,543,847 discloses a seal installation tool which uses the weight of the drill string to initially set the seal and BOP test pressure to apply additional actuation load and activate a lockdown mechanism into an annular groove in the wellhead housing interior.
The A.G. Ahlstone U.S. Pat. No. 3,897,823 discloses a similar structure which utilizes a combination of drill string weight and hydraulic force to set the seal and uses a wedge-type lock against the interior wall of the wellhead housing.